ADP-ribosylation, including poly-ADP-ribosylation (PARylation) and mono-ADP-ribosylation (MARylation), is a multifunctional post-translational modification catalyzed by intracellular ADP-ribosyltransferases (ARTDs or PARPs). Although PARylation has been investigated most thoroughly, the function of MARylation is currently largely undefined. Here, we provide evidences that deficiency of PARP10, a mono-ADP-ribosyltransferase, markedly increased the migration and invasion of tumor cells through regulation of epithelial-mesenchymal transition (EMT), and PARP10 inhibited tumor metastasis in vivo, which was dependent on its enzyme activity. Mechanistically, we found that PARP10 interacted with and mono-ADP-ribosylated Aurora A, and inhibited its kinase activity, thereby regulating its downstream signaling. Moreover, the expression level of PARP10 was downregulated in intrahepatic metastatic hepatocellular carcinoma (HCC) compared with its corresponding primary HCC and adjacent non-tumorous tissues. Taken together, our results indicated that PARP10 has an important role in tumor metastasis suppression via negatively regulation of Aurora A activity.

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Background N-Myc downstream regulated gene 1 (NDRG1) suppresses metastasis in many human malignancies including breast cancer yet has been associated with worse survival in patients with inflammatory breast cancer. The role of NDRG1 in the pathobiology of aggressive breast cancers remains elusive. Methods To study the role of NDRG1 in tumor growth and brain metastasis in vivo, we transplanted cells into cleared mammary fat pads or injected them in tail veins of SCID/Beige mice (n = 7–10 per group). NDRG1 protein expression in patient breast tumors (n = 216) was assessed by immunohistochemical staining. Kaplan-Meier method with 2-sided log-rank test was used to analyze the associations between NDRG1 and time-to-event outcomes. A multivariate Cox regression model was used to determine independent prognostic factors. All statistical tests were 2-sided. Results We generated new sublines that exhibit a distinct propensity to metastasize to the brain. NDRG1-high expressing cells produced more prevalent brain metastases (100% vs 44.4% for NDRG1-low sublines, P = .01, Fisher’s exact test), greater tumor burden, and reduced survival in mice. In aggressive breast cancer cell lines, silencing NDRG1 led to reduced migration, invasion, and tumor-initiating cell subpopulations. In xenograft models, depleting NDRG1 inhibited primary tumor growth and brain metastasis. In patient breast tumors, NDRG1 was associated with aggressiveness: NDRG1-high expression was also associated with shorter overall survival (hazard ratio [HR] = 2.27, 95% confidence interval [CI] = 1.20 to 4.29, P = .009) and breast cancer-specific survival (HR = 2.19, 95% CI = 1.07 to 4.48, P = .03). Multivariable analysis showed NDRG1 to be an independent predictor of overall survival (HR = 2.17; 95% CI = 1.10 to 4.30; P = .03) and breast cancer-specific survival rates (HR = 2.27; 95% CI = 1.05 to 4.92; P = .04). Conclusions We demonstrated that NDRG1 drives tumor progression and brain metastasis in aggressive breast cancers and that NDRG1-high expression correlates with worse clinical outcomes, suggesting that NDRG1 may serve as a therapeutic target and prognostic biomarker in aggressive breast cancers.